1. Field of the Invention
The present invention relates to a projection display apparatus for projecting an mage onto a screen and, in particular, to a projection display apparatus using a reflective light valve such as a Digital Micromirror Device (hereinafter referred to as “DMD”) and a reflective liquid crystal display device.
2. Description of the Related Art
Some conventional projection display apparatuses employ a construction in which light emitted from a light source is led to a light valve through a light tunnel (i.e., a cylindrical optical device). For example, see paragraph 0034 and FIG. 2 of Japanese Patent Application Kokai (Laid-Open) Publication No. 2004-252112 (Patent Document 1). This light tunnel has a tapered portion formed on an incident side so as to continuously decrease the cross sectional area of the tapered portion and a parallel portion formed on an emitting side so as to make the cross-sectional shape of the parallel portion constant. The shape of the cross-sectional shape of the parallel portion and the shape of an emitting end of the light tunnel are formed so as to be similar to the shape (rectangle) of the light valve.
Moreover, there is also proposed a projection display apparatus that determines the positions of corners of the cross-sectional shape of a light intensity equalizing element which equalizes light from a light source in accordance with the positions of corners of a reflective light valve. For example, see Japanese Patent Application Kokai (Laid-Open) Publication No. 2006-189551 (Patent Document 2).
However, for example, when the incident surface (hereinafter referred to as a “surface to be illuminated” or an “image forming area”) of the light valve is not vertically irradiated with light, even if the cross-sectional shape of a light intensity equalizing element is made similar to the shape of the incident surface of the light valve, there is presented a problem that an area actually illuminated (hereinafter referred to as an “actual illumination area”) on the light valve is different in shape from the incident surface of the light valve. This problem is often raised in a case where the incident surface of the light valve cannot be vertically irradiated with the light because of the construction of an optical system, for example, in a case where because of the use of a reflective light valve, a mirror for introducing light to the reflective light valve and a projecting optical system which magnifies and projects the light reflected by the reflective light valve are arranged adjacently to each other.
In the Patent Document 2, the positions of portions (i.e., sides) between the neighboring corners of the cross-sectional shape (or an emitting end surface) of the light intensity equalizing element which equalizes the light from the light source are not specified, so depending on the construction of a projecting optical system, it can be also thought that areas in the vicinity of the middle points of the portions (i.e., sides) between the neighboring corners of the image forming area of the reflective light valve are not suitably illuminated.